Sanding pad



Dec. 20, 1949 T, J, MlLLER 2,491,519

SANDING PAD Filed June 19, 1945 Patented Dec. 20, 1949 SANDING PAD Theodore J. Miller, St. Paul, Minn., assigner to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware Application June 19, 1946, Serial No. 677,881 s claims. (orsi- 189) This invention provides sanding pads or backup pads for use inI the application of coated abrasive sheets in both manual and machine abrading operations. They are particularly adapted for use in reciprocating sanding machines.

An important requirement of such pads is that they conform to the surface being abraded and produce substantially uniform abrasion at all points. A high degree of conformability is particularly necessary in pads used in reciprocating sanders, such as those used in the finishing of automobile bodies where the surfaces being abraded are largely of non-planar contour and where high speeds are desirable, e. g., oscillations that vary from 1800 to 3000 per minute. Heretofore, numerous pads including pads of sponge rubber, cork, etc., spring pads, pneumatic pads and others, have been tried for this type of work, but at such speeds they lack the conformability necessary to avoid the production of high spots on curved surfaces with the consequent high lights and variations in the luster of the finished surface, and have therefore been unsatisfactory.

The pad of the present invention, however, possesses a very nice balance of seemingly opposed qualities, being at once soft, active, agile and highly resilient, and it possesses many desirable characteristics and advantages over the pads previously known, particularly the above described conforrnability and uniformity of abrasion necessary for even sanding of non-'planar surfaces with high speed machines. Even when the present pad is distorted by application to an uneven surface, it continues to produce substantially uniform abrasion on each unit area of the surface that is being abraded. Referring to a preferred embodiment, hereinafter described, one might say that it simulates the human hand, with walls or ribs that approximate fingers so that the pad as a whole produces a series of individually yieldable line contacts between the sandpaper and a workpiece opposite the walls. The term line contact refers to increased pressure of the sandpaper against the work along a narrow strip or line, as contrasted with flat or surface contact wherein the pressure is uniform over a comparatively Wide area.

The pad also increases the cutting ability of the sandpaper many times which is due, at least in part, to the iiexing action and relative movement of the mineral particles which occurs as the sandpaper is used. As the pad moves over an uneven 'surface and distorts, the sandpaper is flexed with it, moving up and down, in and out, alternately at various points in its area, thus yare rounded, as at l5.

opening up its coating of grits and binder so as erally parallel to the sanding surface.

The inventionis exemplified by pads described hereinafter and illustrated in the accompanying drawings, in which Figures l and 2 are plan and side elevational views, respectively, of a preferred form of a pad made in accordance with the present invention;

Figures 3 and 4 are framgentary side elevational views showing alternative shapes for the ends of the pad;

Figures 5 and 6 are fragmentary side elevational views showing alternative transverse shapes for the cavities;

Figures 'l and 8 are plan views showing alternativev patterns for the series of cavities; and

Figures 9 and 10 are end and side elevational views, respectively, of a reciprocating sanding machine equipped with pads of the present invention.

The pad of Figures 1 and 2 comprises a rectangular shaped body portion I0 of natural sponge rubber, relatively thin in proportion to length and breadth, having a generally planar bottom or under surface il (referred to herein as the face) adjacent to which the sandpaper is fixed when the pad is in use, and a top or upper surface I2 which contacts the pad holder or shoe of the, sanding machine in which the pad is used. Threaded pegs or screws I3, suitably fixed to the lpad (as by attachment of their lower ends to a metal plate or other anchor embedded in the pad) and extending upwardly therefrom, provide means for attaching the pad to the machine. These may be omitted (as in Figures 3 and 4) and the pad attached by other means; for example, the pad may be held in place by the tension of the sandpaper that is wrapped around it and clamped to the shoe. Ridges or beads i4 on the upper edges of the ends of the pad iFigure 3) designed to fit around corresponding edges or ends of the shoe to act as bumpers, maybe employed if desired. Similar bumpers may be placed Aon the sides, as well. The lower edges of the ends Alternatively, they may beiof other shapes, e. g., they may be sharply angular or pointed, as at I' in Figure 4. The latter shape facilitates reaching corners, edges, etc., as in the reveal or quarter panel as well as the roof next to the drip rail of an automobile body. i

'I'he body of the pad is pierced by a series of tubular shaped holes or perforations or -bores I6, circular in cross section, which extend between the sides Il substantially parallel to each other and to the face II. The holes or bores extend at an angle of approximately in respect to the pads axis of operation, i. e., the direction of movement or reciprocation of the pad, the said direction being indicated by the arrows in Figure 1. In the illustrated pad this axis coincides with the pads short or transverse axis. The said angle of the holes or bores may vary from 0 to 90, the preferred range being from about 5 to 30 `in pads 0f the illustrated dimensions.

The minimum angle of the ypreferred range is that which would position the far end of the bore to the right (-or left) a distance of at least one full diameter in respect to the near end of the bore. Such lan angle would obviously vary in terms of degrees with the length and diameter `of the bore. A lesser angle tends to produce pattern in the work (a regularly occurring unevenness in the abrading) since in any given stroke, certain portions of the surface being Qjabraded would not be pressed by a fingen i. e., `a rib or wall-supported portion of the pad, which is theportion of the pad opposite the walls I8 that are between each bore.

The maximum angle of the preferred range is that at which the face II and the upper surface I2 of the pad will `continue to move in approximate unison when the pad is reciprocated. As the angle widens and the reciprocating impulses become more nearly cross-wise of the bores, distortion of the pad begins, i. e., the walls or ribs that separate the bores tend to bend, with the result that the face of the pad reciprocates less than the upper surface and the cutting eiciency is reduced.

The bores or cavities are preferably curvilinear in cross section, such vas circular (Figure 2), crescent shaped (Figure 5), oval or elliptical (Figure 6), etc., as contrasted `With straight sided shapes such as squares, oblongs, triangles, etc., although straight sided shapes may be used, particularly those that would make the ibores roughly or generally tubular, such as octagons, decagons, etc. A bore need not be of the same size or cross section throughout its length nor need all the bores be uniform in size or cross section.

The size of the bores and theirnumber and spacing from each other and from the face of the pad are adjusted to -provide ,the pad with the optimum conform-ability to surfaces being abraded in accordance with the size of the pad and the natural yieldability, resilience, density, etc. of the material from which the pad is made'. Generally, it is preferred that the bores be in relatively close spaced relation to each other and to the face, with the thickness of the ribs or walls between the bores, and between the bores and the face, less than half the laverage cross diameter of ,the cavities, although thicker walls may be used without losing the advantages of this invention.

The dimensions and proportions of the pad and of its parts may vary widely.

The illustrated pads, of natural sponge rubber,

bores are 11g" apart and 1A," from the face.

`length and breadth of the pad is of course governed by the size of the shoe or pad holder on the fnzichine. The illustrated pad measures 31/2 x ,f' 6 4l)- or ribs I9 between the bores and the face II is (approximately 1/8 thick. In other words, the The The bores are preferably approximately parallel to the face but they need not always be parallel to each other nor spaced an equal distance apart. The longitudinal axes of the bores of the illustrated pads are straight but they may curve, as in Figure 7, or otherwise vary from a straight line, if desired.

The cavities I6 need not always pierce the pad (i. e., extend clear through it) but may extend part way, with either or both ends of some or all of the cavities closed. They need not all be parallel to each other, nor of equal length. Thus the series of cavities may form a variety of patterns, such as the herringbone pattern shown in Figure 8, and other patterns, it being preferable that the series of cavities as a whole be substantially coextensive with andl substantially parallel to the face of the pad.

Advantages of having bores that pierce the pad, as in the illustrated embodiment, include ease of'manufacture, 'and a reduction in resistlance and in splashing in Wet abrading operations, some of the abrading lubricant nding its way into the open bores when the pad is moved against it The illustrated pads are of natural sponge rubber but they have a relatively impervious outer surface due to the outside skin that is formed during molding. The face II has a knurled surface (or it may be a cloth-embossed surface) which provides vents for the gases that form within the pad while in the mold, and which helps to keep the sandpaper from slipping when the pad is in use. The said knurled or clothembossed surfaces of the face II may be formed during the molding by complementary markings on, or by a sheet of canvas adhered to, the corresponding f-ace of the mold, respectively.

Synthetic sponge rubber may also be employed,

and solid rubber, either natural or synthetic, as

well as other materials which will have the required softness, agility and resilience when shaped in accordance with this invention.

When made from oil-resistant substances such as oil-resistant synthetic rubber, the pads can be used for furniture and other types of sanding where oil lubricants are used.

The softness and resilience of the pad may be varied and controlled by the density of the material, e. g., by the density of the rubber, varying from soft sponge to solid rubber.

The illustrated pads are generally planar or flat, but they may be curved, angular or of other shapes as well, to conform to the machine for which they may be designed, or to the workpiece to be abraded, etc.L

Figures 9 and 10 illustrate the pads in use on a high speed reciprocating sanding or rubbing machine of the type sold under the trade name Sundstrand and described in Anderson Patents Nos. 1,524,902 and 1,677,112 and Ekstrom Patent No. 1,590,353.

Two pads I are fixed to pad holders or shoes 2i which are reciprocated alternately away or apart from each other and then toward each other (as indicated by the arrows) by a compressed air mechanism in the body portion 22 of the machine, the air being conducted thereto by the tube 23. The faces Il of the pads i0 are covered with sheets of sandpaper S which are held in place by clamps 20.

y In operation, the machine is held by the operator with the 'abrasive covered pads applied against a surface to be abraded. Pressure on the handle 24 sets the machine in motion, causing the pads to oscillate orreciprocate and thereby to abrade the workpiece.

I claim:

l. A sanding pad comprising a body of resilient material having a continuous working face and a series of elongated cavities extending into said body from opposite sides thereof and spaced with respect to said working face and each other so thatk the minimum thickness oi said resilient material in said working face and in the walls between said cavities is not more than one-half of the greatest internal dimension of said cavities normal to the longitudinal axis thereof, said walls between said cavities in the lengthwise direction thereof being sopositioned, relative to the axis of operation of said sanding pad, as to diverge therefrom in the length of said cavities by a distance not less than the greatest width of the openings in the sides of said sanding pad o! the cavities adjacent to each such wall, but at no place diverging at an angle to said axis of operation greater than approximately 30.

2. A sanding pad comprising a body portion oi resilient material having a series of tubular shaped cavities extending from one extremity of the body to the other at an angle of from approximately 5 to 30 in respect to the pads axis of operation. in relatively close spaced relationship to each other and to the face oi.' the pad and subatantially parallel to each other and to the face.

3. A soft, active, resilient sanding pad comprising a body portion of resilient material. rectangular in shape and relativelyrthin in proportion to length and breadth, pierced with a series of tubular bores oi circular cro section extending from one side or the pad to the other at an angle of 'from 5 to 30 in respect to the pads axis oi operation substantially parallel to each other and to the face of the pad, the thickness of the walls which intervene between the bores and between the bores and the face being less than half the diameter of the bores.

4. A soft, active, resilient sanding pad coxnprising a body portion of sponge rubber. rectanguiar in shape and relatively thin in proportion to length and breadth, pierced with a series of tubular bores of circular cross section extending from one side of the pad to the other at an angle of from 5 to 30 in respect to the pads axis of operation substantially parallel to each other and to the face of the pad, the thickness of the walls which intervene between the bores and between the bores and the face being less than half the diameter of the bores.

5. A sanding pad comprising a body portion of resilient material measuring approximately 6%" long by 31/2" wide by li" thick pierced with a series of straight tubular bores of circularI cross section approximately 1/2" in diameter extending from one side of the pad to the other at an angle of approximately 20 in respect to the pads short axis, substantially parallel to each other and to the face of the pad and spaced approximately 11;" apart and M," from the face.

6. A soft, active, resilient sanding pad, comprising a body portion of sponge rubber measuring approximately 6%" long by 3%" wide by l" thick pierced with a series of straight tubular bores oi circular cross section approximately l/2" in diameter extending from one side of the pad to the other at an angleof approximately 20 in respect to the pads short axis, substantially parallel to each other and to the face ot the i pad and spaced approximately apart and 5i" from the face.

THEODORE J. hmmm.

' REFERENCES errno The following references are of record in the ille of this patent: i

UNITED STATES PATENTS Number Name Date 1,175,245 Dennis Mar. 14, 1916 1,896,946 Gauss Peb. 7. 1933 2,224,140 Champayne Dec. 10, 1940 2,242,545 Randolph May 20. 1941 2,877,880 Gutsell June 13, 1945 

